The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Ice accretion on the surfaces of machines or devices that separate flows of gases, such as air, into a primary and a secondary flow, e.g., surfaces of a turbomachine, can cause mechanical and safety issues regarding the respective machine or device. For example, this type of separator is found especially in the inlet compressor of a dual rotor axial turbomachine. In this type of machine, the flow of incoming air is separated into a primary and a secondary flow. The primary flow, generally annular in cross-section, passes through the engine's different compression stages, the combustion chamber and turbine. The secondary flow, generally annular in cross-section and of a greater diameter than the primary flow and concentric with the primary flow, is compressed by the fan and the secondary flow stators and then rejoins the main flow, contributing to the thrust.
The secondary flow separated from the main airflow after passing through the inlet fan can cause the leading edges of the secondary airstream guide surfaces to ice up. This airstream is not subject to any heating and its defining boundary walls are relatively far from the machine's heat sources. In certain conditions (cold air having a high humidity) the air may contain supercooled water droplets which solidify on contact with the leading edges, the latter then providing accretion surfaces where icing can occur. This phenomenon is particularly common at the primary and secondary stream splitter nose, specifically at the leading edge and the boundary wall defining the secondary flow close to the leading edge.
United States patent application US/2003/0035719 A1 discusses the problem of icing on the leading edge of the splitter nose. The proposed solution in US/2003/0035719 is to provide clearance at the mechanical joint between the leading edge and the wall defining the primary stream, and to inject a stream of hot air in the cavity formed by the splitter nose. Because of this clearance, the hot air can flow along the mechanical joint at the leading edge and escape. This flow ensures a supply of thermal energy close to the leading edge. An alternative described in US/2003/0035719 is to provide an additional wall in the secondary airflow. The nose is designed so that the flow of hot air also escapes onto the additional wall. The flow of hot air comes from the high pressure compressor. The solution proposed by this interpretation has two major drawbacks, namely the complexity of the hot air feeder device and the loss of power due to this leakage flow (energy required to compress the airflow does not contribute to the thrust).
Patent GB 2,406,142 A also addresses the problem of icing on the leading edge and the first row of stator blades. The proposed solution in GB 2,406,142 is to provide a heat pipe connecting a heat source located further downstream in the machine with the splitter nose. Although the effective thermal conductivity of a heat pipe is high, especially in comparison with a material such as copper, this solution is nevertheless expensive and complicated because a number of heat pipes distributed over the circumference of the splitter nose are necessary to ensure effective de-icing.
Patent EP 2075194 A1 relates to an air-oil heat exchanger located at the splitter nose and close to the leading edge. The presence of the heat exchanger near the leading edge has the double advantage of forming a heat source to prevent icing as well as providing high efficiency heat exchange. However, it has drawbacks as it is technically complex. This solution also presents a significant risk of damage to the exchanger and oil leakages when the machine ingests a foreign body, because of the very forward position of the exchanger.
Patent EP 1895 141 A2 also relates to an air-oil heat exchanger located at the splitter nose and close to the leading edge. The most forward part of the splitter nose together with the walls of the nose forms an internal volume covered by a lubricant for cooling. This configuration prevents ice forming because of the heat supplied by the lubricant. As in EP 2075194 A, this arrangement is technically complex and likely to suffer from failures, especially leakage of the lubricant when the machine ingests a foreign body.